I have the core rulebook for
GURPS Prime Directive (the one made for
GURPS 4th Edition), as well as faction books for the Federation, Klingons, and Romulans. Mostly, I use them as background sources, since I don't have an RPG group to hand.
If you wanted to give
Prime Directive a try, it's currently supported in both
GURPS 4e and
D20 Modern editions, plus there'll be a Mongoose
Traveller edition published at some point (hopefully this year). You can find some older editions (the original
PD1, which had its own home-grown game engine, as well as editions for
GURPS 3e and
D20); but those are no longer actively supported.
I should note that these are set in the Star Fleet Universe, as opposed to the Paramount/CBS Franchise; so things wil be rather different to what you'd get in works created under a different licence. (So when I say I use them for background data, I mean data relevant to ADB's universe in particular.) If the SFU isn't your thing,
Prime Directive might not be of much use for you.